Derivative Instruments - Summary of Average Monthly Notional Value of Future Contracts Outstanding (Detail) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Weighted Average [Member] \| Commodity Futures Contract [Member]
Derivative [Line Items]
Average Notional Value	$ 1,998,989,924	$ 2,280,292,516	$ 2,228,834,272	$ 2,121,983,429

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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